This invention relates to lid designs for laboratory sample containers (e.g., microcentrifuge tubes) which facilitate their opening.
Microcentrifuge tubes are small plastic tubes which are typically tapered, conical or rounded, and closed at one end. The tubes are capable of holding 0.4-2.0 ml liquid, and are constructed to withstand forces typically in excess of 10,000 times their own weight (10,000.times. g) during centrifugation. These tubes are used widely in biotechnology laboratories as vessels for handling radioisotope chemicals, for storing biochemicals, for performing biochemical reactions, and for handling sterile contaminant-free samples. They have tight fitting lids whose size and shape protect and cover the perimeter of the tube opening, and help maintain the inside of the tube in an aseptic condition. The lids are generally attached to the tubes by a flexible hinge and are sealed to the tube by pressing them downward against a resisting frictional force. In this sealing process, the annular sealing portion of the underside of the lid, shaped to a sealing fit inside the tube opening, is forced downward into the tube and compressed. The lids are secured against accidental opening by a number of means which vary in effectiveness, including friction force-fit of the lid in the tube, integrated lid "catches" which secure the lid (or secure a lid over-cover) to a lip flange provided on the tube, or alternatively, by separate lid clamps which may be slid or snapped into place after the lid has been closed. Examples of such tubes are described and advertised for sale in the current 1992-1993 scientific apparatus catalogs published by VWR Scientific (pp. 320-323), and Curtin Matheson Scientific (pp. 11/260-11/263) hereby incorporated by reference.
For subsequently aiding in unseating and opening the sealed, or sealed and secured lid, the generally flat lid opposite the lid hinge is usually extended horizontally beyond the outer diameter of the tube's lip flange to provide a standard lifting tab. A thumb, thumbnail or opener device may be used to lift upward on this tab. Warburg, U.S. Pat. No. 4,858,502 describes a specialized opener tool designed to open the microcentrifuge tube. The tool contains a recess space and other features shaped to engage the lid's lifting tab thereby allowing the tube to be opened.
In the process of opening the microcentrifuge tube, finger and/or tool-contact with the underside of the lid lifting tab may contribute to contamination of the sample in the tube. For example, Applicant has discovered that when a finger or fingernail is inserted beneath the lifting tab and pressure is applied upward on the lid, as the lid opens, the finger and/or fingernail may inadvertently contact the annular sealing portion of the underside of the lid. Analysis of the relative motions of the finger, e.g., thumb, and the lid during opening of the tube shows that as the lid "snaps" open and pivots backward on its hinge, the rapidly diminishing contact angle between the rotating lid and the finger causes such undesirable inadvertent contact. Subsequent reclosing of the lid can introduce contaminants from the finger into the tube. Even the use of surgical gloves cannot assure that cross-contamination between successively opened microcentrifuge tubes will not occur. The container opener tool of Warburg in U.S. Pat. No. 4,858,502 reduces the incidence of contamination of microcentrifuge tube samples during the process of opening the tubes. Applicant has found, however, that when a trace of liquid or other contaminant substance is introduced into the recess of the Warburg device, this substance may be transferred to the underside of the lid lifting tab. From this location, during the subsequent closing of the tube and contact between the lip of the tube and underside of the lid, migration of the contaminant into the tube is possible.